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Appendix II.


With friction, the real resistance is R2, and the force diagram
A B D, where 0 = friction angle.

W ^ A B _         i    '

Po         BD

tan (0 + 0)
P          tan 9

P2      tan (0 + 0)

shewing that large pitch is economical.    Returning to the experi-

and efficiency ==


/n      x       tan 0
tan (0 + 0)  = -_- =
effy. "•

•. 0 = (0 + 0)~ 0 = 13*27°-476° = 8-51°

and   IJL — tan 0 = "1494       (Seep. 1125.)

Absorption Dynamometer.— The apparatus in
Fig. 596 is called an Appold 'brake. If P = pull on stud D,
r = radius of brake wheel, and Fn total friction on "brake strap,
the sum of moments being necessarily zero,

(W-S)R ± (PxAD) = Fnr

or the total moment exerted by the-.engine. P may be measured
by two spring balances, one on each side of D, a pull on the right
balance being plus, and on the left minus. The work absorbed
per revolution would be          • ' '

2 ^{(w - S)R ± (P x A D)}

whence B.H.P. is found. If the H.P. be under 15 and the
lubrication sparing, there is little pull on r>, but the lever is
generally a bad arrangement, and a simple strap is now advised,
where only W and S are measured.

P. 580. Distribution of Power.^—We may distinguish
between mere transmission, and distribution from a central station
to many consumers. Professor Unwin has shewn the advantages
of the latter over individual installations, and gives the following

i. Indefinite subdivision and measurement.

af. Minimum first cost and mntxing- loss.           '                    *

3. Freedom from danger.                                         • • . i

3 -M